An electric double-layer capacitor is an electric storage device applying to storage of electricity a phenomenon in which layers (an electric double-layer), each having positively or negatively charged ions arrayed therein at extremely short distances, are formed in interfaces, in each of which two different phases contact each other as with a solid-state electrode and an electrolytic solution. This electric double-layer capacitor has an extremely large capacitance from several tens of milli-farads to several thousands of farads or more and has characteristics which are an excellent charge and discharge cycle (life) and an excellent rapid charge and discharge. Therefore, the electric double-layer capacitor is used as a back-up power source which is a power supply source for retaining operations of a real-time clock and a memory IC while a power source of an apparatus is turned off or as a power source for power assist and power supply, used upon activating and operating an actuator motor or the like of an apparatus.
As shown in FIG. 9 and FIG. 10, an electric double-layer capacitor Y has a configuration in which a capacitor element 8 impregnated with an electrolytic solution is housed in a case 90 and an upper opening 91 of the case 90 is sealed with an insulating member 92.
As is seen from FIG. 11 and FIG. 12(a), the capacitor element 8 has a configuration in which a positive electrode body 80, a separator 81, a negative electrode body 82, and a separator 83 are stacked in this order and are wound in a cylindrically-shaped manner. The positive electrode body 80 has a configuration in which two positive electrode current collectors 84A and 85A having polarized electrode layers 86A and 87A formed respectively thereon are caused to contact each other such that surfaces of the positive electrode current collectors 84A and 85A, on which the polarized electrode layers 86A and 87A are not formed, contact each other. The negative electrode body 82 has a configuration in which two negative electrode current collectors 84B and 85B having polarized electrode layers 86B and 87B formed respectively thereon are caused to contact each other, as with the positive electrode body 80.
As shown in FIG. 10 and FIG. 12(b), the positive electrode body 80 further has an external terminal 93A fixed in the insulating member 92 and positive electrode tabs 88A and 89A for allowing conduction with the positive electrode current collectors 84A and 85A. The positive electrode tabs 88A and 89A are attached onto surfaces of the positive electrode current collectors 84A and 85A, on which the polarized electrode layers 86A and 87A are not formed.
As shown in FIG. 10 and FIG. 12(c), the negative electrode body 82 further has an external terminal 93B fixed in the insulating member 92 and negative electrode tabs 88B and 89B for allowing conduction with the negative electrode current collectors 84B and 85B, as with the positive electrode body 80. The negative electrode tabs 88B and 89B are attached onto surfaces of the negative electrode current collectors 84B and 85B, on which the polarized electrode layers 86B and 87B are not formed.
As shown in FIG. 12(b), FIG. 12(c), and FIG. 13, the positive electrode tabs 88A and 89A or the negative electrode tabs 88B and 89B are in contact with and paired with each other in a corresponding relationship without being displaced (for example, refer to Patent Literature 1).
In the capacitor element 8, since the larger the number of the tabs 88A, 88B, 89A, and 89B is, the larger an increase in current collecting points is, thereby reducing an internal resistance, a larger number of the tabs 88A, 88B, 89A, and 89B is preferable. Therefore, as shown in FIG. 9, FIG. 10, FIG. 12(b), and FIG. 12(c), there also available is a capacitor element 8 which includes a plurality of tabs 88A, 88B, 89A, and 89B in a positive electrode body 80 and a negative electrode body 82, respectively (for example, refer to Patent Literature 2). On the other hand, in the configuration in which the tabs 88A and 88B, 89A, and 89B are in contact with each other, respectively without being displaced, when the number of the tabs 88A, 88B, 89A, and 89B is large, as is understood from FIG. 13, due to the influences of thicknesses of the tabs 88A, 88B, 89A, and 89B, the capacitor element 8 becomes out of roundness, and therefore, there is a limit to the number of the tabs 88A, 88B, 89A, and 89B. For example, in a capacitor element 8 in which metal foil as current collectors each having a thickness of approximately 20 to 50 μm and tabs each having a thickness of approximately 100 to 200 μm are used, the number of pairs of the tabs 88A, 88B, 89A, and 89B is approximately two in one side of the electrodes in a small-sized device (φ35) (the total number of tabs is four on the one side of the electrodes) or approximately four on one side of the electrodes in a device having φ51 or more (the total number of tabs is eight on the one side of the electrodes).
In addition, in the configuration in which the tabs 88A and 88B, 89A, and 89B are in contact with each other, respectively without being displaced, thicknesses of respective two pieces among the tabs 88A, 88B, 89A, and 89B are concentrated in one portion, thereby leading to a problem in that a large stress is exerted also on the positive electrode body 80, the negative electrode body 82, and the separators 81 and 83.